Among the recent vehicles, vehicles which perform so-called “idle stop” of automatically stopping an engine while the vehicle is stopped have been increasing for fuel consumption enhancement. Automatic stop (idle stop) of an engine is performed when a predetermined automatic stop initiating condition is established. Generally, the automatic stop initiating condition is established, when all of predetermined requirements are satisfied. For instance, the automatic stop initiating condition is established, when all the requirements such as the vehicle speed is zero (i.e. the vehicle is stopped), a braking operation is performed, an acceleration operation is not performed, and the transmission is in a neutral state are satisfied.
Further, a predetermined automatic stop cancelling condition is set in order to automatically restart the engine that has been automatically stopped. Generally, the automatic stop cancelling condition is established when one or more requirements included in the automatic stop initiating condition is not satisfied (e.g. when the accelerator pedal is stepped on, or when a braking operation is released).
The automatic stop initiating condition of an engine is not always related to a driver's operation. For instance, when a battery charging amount is less, when a battery power consumption is large, when an engine coolant temperature or the engine oil temperature is low, when an oil temperature or a hydraulic pressure of the transmission is low, or when a difference between a preset temperature and an actual temperature of the air-conditioner is large (i.e. the air-conditioning request level is high), it is preferable not to perform automatic engine stop. When one or more of the aforementioned statuses is observed, it is desirable to prohibit automatic engine stop, even if all the requirements based on a driver's operation are satisfied.
As described above, automatic engine stop is prohibited by a variety of requirements that do not result from a driver's operation. Therefore, it is not easy for the driver to recognize in what condition automatic engine stop is prohibited. As a result, when automatic engine stop is not performed even though the vehicle is stopped, some of the drivers may be worried that the automatic stop device is out of order. Further, some of the drivers may be worried that automatic engine stop is not performed because of an inappropriate driver's operation while the vehicle is stopped, and may perform an unnecessary operation such as a hard braking operation.
The aforementioned phenomena may also occur when the engine is automatically restarted regardless of the absence of a driver's operation. For instance, automatic engine restart may be performed because of lowering of battery charging amount while the engine is automatically stopped. In such a case, the engine may be automatically restarted regardless of the absence of a driver's will to start. In this case, the driver may also be worried that the automatic stop device is out of order.
Further, automatic engine stop may be frequently prohibited, or an automatic engine stop time may be exceedingly shortened (i.e. the engine may be restarted immediately after automatic engine stop) due to some trouble of the vehicle. At the time of maintenance service of the vehicle, the maintenance engineer may be forced to check the presence or absence of such a trouble.
Patent Literature 1 discloses a self diagnosis device for an automatic stop device for an engine so as to appropriately perform automatic engine stop or automatic engine restart. However, Patent Literature 1 has failed to solve the aforementioned drawbacks.